1. Field of the Invention
This invention is in the field of biological therapeutics. In particular, the invention relates to biopolymer conjugates comprising an analog or mutant of human interleukin-11 (mIL-11), where the mIL-11 exhibits enhanced stability as compared to a mature recombinant human IL-11 (rhIL-11), and where the biopolymer conjugate retains substantially the same level of activity as mIL-11.
2. Background Art
Hematological toxicity, as manifested by neutropenia and thrombocytopenia, is an unwanted side effect associated with cancer chemotherapy, often restricting the dose of anti-tumor drugs being administered to a patient. The administration in vivo of interleukin 11 (IL-11), a stromal cell-derived cytokine which interacts with a variety of hematopoietic and non-hematopoietic cell types, has been shown to increase platelet count and have a beneficial thrombopoietin effect. IL-11 plays a major role in the differentiation of stem cells into megakaryocytes, the proliferation and maturation of megakaryocytes, and the generation of platelets.
Recombinant human IL-11 (rhIL-11) has potential utility in the treatment of side effects associated with cancer chemotherapy. When administered to animals, rhIL-11 enhances megakaryocytopoiesis and increases platelet counts in both normal and immunosuppressed animals. An rhIL-11 product is marketed by Wyeth-Ayerst as NEUMEGA® (generic name oprelvekin) and is approved for the prevention of severe thrombocytopenia and the reduction of the need for platelet transfusions following myelosuppressive chemotherapy in adult patients with nonmyeloid malignancies who are at high risk of severe thrombocytopenia. NEUMEGA® is supplied in a single use vial containing 5 mg IL-11 as a lyophilized powder. The powder is reconstituted with 1 mL sterile water for injection, USP, to produce a solution comprising 5 mg/mL IL-11 which is administered at a dose of 50 μg/kg/day. The most frequent adverse events associated with NEUMEGA® include atrial arrhythmias, syncope, dyspnea, congestive heart failure, and pulmonary edema.
Although the administration of rhIL-11 in vivo has been shown to have a demonstrable pharmacological effect towards preventing the reduction of platelet count in patients undergoing cancer chemotherapy, the required frequency of administration (often once a day for two weeks or more) is higher than desirable. Furthermore, while cytokines such as IL-11 are attractive therapeutic agents, their use is often restricted due to their rapid clearance through urinary excretion, hepatic uptake, and/or enzymatic degradation. The kidney and liver appear to be major contributors to the rapid clearance of rhIL-11 from the circulation of an animal. This rapid clearance is likely due to the low molecular weight of rhIL-11 (approximately 19 kDa) and its highly cationic character. Since the permselectivity of the glomerular capillary wall to macromolecules is based primarily upon molecular size, chemical modifications of rhIL-11 with water-soluble polymers could restrict the glomerular filtration of the protein.
Modification of recombinant proteins with biopolymers such as polyethylene glycol (PEG) molecules has been studied as a means of addressing the short circulation time. The conjugation of PEG polymer to proteins (PEGylation) has been shown to improve the bioavailability by increasing the hydrodynamic radius of proteins thus protecting from rapid renal clearance and to increase solubility. Moreover, due to the bulkiness of PEG polymers, the PEG conjugated proteins exhibit reduced proteolysis, and reduced immune recognition, which confer substantial advantages of the PEGylated proteins (Veronese F M and Pasut G., Drug Discovery Today 10:1451-8 (2005)). On the other hand, the capacity for a PEG conjugated protein to prevent its susceptibility to proteolytic enzymes or antibodies can also hamper the protein's ability to bind to its receptor. As result the binding affinity of a PEG conjugated protein to a receptor would be reduced, especially if the conjugation site is involved in or is in close proximity to the receptor binding site.
To address the need for retaining rhIL-11 in the circulation, researchers have investigated the feasibility of chemically modifying rhIL-11 with the water-soluble polymer polyethylene glycol (PEG). See Takagi et al., Journal of Controlled Release 119: 271-278 (2007). However, as described above, chemical modification of rhIL-11 with PEG has numerous disadvantages. Due to the bulkiness and steric hindrance of the attached PEG, a PEG-rhIL-11 conjugate could fail or minimally bind to the IL-11 receptor. Furthermore, the biological activity of the rhIL-11 molecule could be reduced. In fact, Takagi et al. demonstrated that while PEG-rhIL-11 conjugates were retained in the plasma for a longer period of time than an unconjugated rhIL-11 and thus resulted in a measurable effect on the increase of platelet count, the remaining biological activity of PEGylated-rhIL-11 was decreased by the conjugation to PEG. Takagi et al., Journal of Controlled Release 119: 271-278 (2007). Therefore to achieve the targeted efficacy, an increased amount of PEG-rhIL-11 conjugate was required to be administered.
The present invention addresses the need for an IL-11 molecule that, when administered to patients, is not only retained in the plasma for a longer period of time, but also retains biological activity, thereby increasing its efficacy for the treatment and prevention of thrombocytopenia and other hematological toxicities associated with cancer chemotherapy.